As known, an optical projection system is widely applied to presentation and entertainment. Generally, a light uniforming device is employed in an optical projection system to collect the input light emitted from a light source and uniformize brightness distribution of the light at the output. At present, the light uniforming device is known as a light tunnel. The light tunnel can be utilized to uniformly and precisely project light passing therethrough to an effective area of a light source modulating device to prevent uninformed brightness at a particular light path of the light engine.
FIG. 1A is a schematic view of a conventional light tunnel; and FIG. 1B is a cross-sectional view of the light tunnel along line A-A of FIG. 1A. As shown in FIG. 1A and FIG. 1B, the light tunnel 1 is a hollow cuboid structure formed by connecting four stripped reflecting plates (i.e. mirror) including a top reflecting plate 11, a bottom reflecting plate 12, a right reflecting plate 13 and a left reflecting plate 14. To assemble the light tunnel 1, each reflecting plate is connected to an adjacent reflecting plate at edge. By abutting the right reflecting plate 13 and the left reflecting plate 14 against the top reflecting plate 11 and the bottom reflecting plate 12, a light passage 15 with a light entrance 16 and a light exit (not shown) is formed. An adhesive 9, for example epoxy, silicon rubber or ultra-violet (UV)-curved adhesive, is applied at the external junctions of the connected reflecting plates 11, 12, 13 and 14 so that the top reflecting plate 11, the bottom reflecting plate 12, the right reflecting plate 13 and the left reflecting plate 14 can be connected together to form the light tunnel 1.
FIG. 2 is a flowchart showing the process of manufacturing the conventional light tunnel. Referring to FIGS. 1A, 1B and 2, the process of manufacturing the conventional light tunnel 1 is described as below. Firstly, at the step S1, four reflecting plates are formed. The four reflecting plates include a top reflecting plate 11, a bottom reflecting plate 12, a right reflecting plate 13 and a left reflecting plate 14, and all of the top reflecting plate 11, the bottom reflecting plate 12, the right reflecting plate 13 and the left reflecting plate 14 are rectangular solid components. Then, at the step S2, the top reflecting plate 11, the bottom reflecting plate 12, the right reflecting plate 13 and the left reflecting plate 14 are assembled together to form the light tunnel 1.
At the step S1, the process of forming the top reflecting plate 11, the bottom reflecting plate 12, the right reflecting plate 13 and the left reflecting plate 14 includes the following sub-steps. Firstly, at the step S11, a glass plate coated with a film is provided. Then, at the step S12, the glass plate with the film is cut by performing a cutting process so that four stripped reflecting plates are formed. The four reflecting plates include the top reflecting plate 11, the bottom reflecting plate 12, the right reflecting plate 13 and the left reflecting plate 14. Each of the top reflecting plate 11, the bottom reflecting plate 12, the right reflecting plate 13 and the left reflecting plate 14 is a rectangular solid component and has six surfaces, wherein any two adjoined surfaces of the respective reflecting plate are perpendicular with each other.
Due to that each of the top reflecting plate 11, the bottom reflecting plate 12, the right reflecting plate 13 and the left reflecting plate 14 is a rectangular solid component, any two adjoined surfaces of the six surfaces of the respective reflecting plate are perpendicular with each other. When the top reflecting plate 11, the bottom reflecting plate 12, the right reflecting plate 13 and the left reflecting plate 14 are assembled to form the light tunnel 1 and a light passage 15 of the light tunnel 1 having a non-rectangular cross section is required, the left reflecting plate 14 must be obliquely disposed between the top reflecting plate 11 and the bottom reflecting plate 12 to form the light passage 15 having a non-rectangular cross section, as shown in FIG. 1B. However, there will be a gap (i.e. clearance) 17 formed at a junction between a first surface 141 of the left reflecting plate 14 and a bottom surface 111 (i.e. inner surface) of the top reflecting plate 11 due to that the left reflecting plate 14 is a rectangular solid component. Namely, an acute angle is formed between the first surface 141 of the left reflecting plate 14 and the bottom surface 111 of the top reflecting plate 11. The gap 17 will result in the brightness degradation to deteriorate optical quality of the light tunnel 1 and dark lines formed on the display image to degenerate the image quality of the optical projection system.